The original Mount and Blade: Warband by itself is hilariously fun with chaotic multiplayer and the ability to customize your chosen class and including its several gamemodes, but NWs is EVEN MORE CHAOTIC BY FAR.
Long-range firefights are now quite common, many, many classes are available PER NATION, the new maps are quite nice, cavalry is still seemingly inevitable to destroy your lines, arm and bear several artillery pieces against your foes, and simply blow the heck out of forts. A massive melea or charge effort is always going to occur around every step. THIS OFFICIAL MULTIPLAYER MOD IS BY FAR CHAOS, CHAOS, AND MORE CHAOS!!!
NEW FEATURES: Obviously the maps are new to it. There are several fun maps to choose from, with several different styles, etc. Also, buildings can be destroyed by explosive attacks from artillery in the game, so don't expect to be invincible in them.
Another neat feature is the engineer/sappers classes. They allow you to build your own fortifications anywhere and however you like (requiring buildpoints as the drawback). Sappers are essential in Siege Battles to patch up those destructable walls and breaches....
As for Sieges, they are insanely fun and always full of action and constant pushes to overwhelm the defenders' defences. Firefights and artillery are always a major danger for either side. Watch as your comrades that are slightly ahead of you get mowed down by defending fire as they enter a breach. SIEGES IN THIS GAME ARE VERY FUN TO FOOL AROUND WITH, SO DON'T HESITATE TO TRY 'EM!
As for the Mount and Blade: Warband - Napoleonic Wars' COMMUNITY goes, it is quite decent. The fact they have EVEN MORE IN-DEPTH AND MORE MODERN-LIKE MILITARY RPGing and Regiments make the Regimental/Clan EXPERIENCE almost THRICE as good as the original clan combat (of course if you like constantly meleaing with enemies as always).
If you are lucky, you can find an amazing group of people that host immense battles including many different regiments at the same time per team, with a sole or several main leaders for that entire team (RPG!, RPG!).